Mobile telecommunications networks are usually arranged according to a cellular structure comprising a plurality of cells, each cell being defined as the set of elementary territory areas (also referred to as “pixels”) served by the radio-electric signal radiated from a respective Base Radio Station (BRS), or antenna.
Among the known cellular networks, networks using the CDMA or WCDMA technique have the peculiarity that a same frequency band (or “channel”) can be re-used in the various cells. Therefore, the passage of a mobile communications terminal from one cell to another, contiguous cell (an event called “handover”) can be managed by using the same frequency, according to a mechanism called “soft-handover”; this mechanism provides that, in particular geographic areas, called “soft-handover areas” or “macro-diversity areas”, the mobile communications terminal is able to decode signals from (and therefore to exchange information with) many antennas and, consequently, with many BRSs.
The location of the macro-diversity areas and their dimensioning are highly important factors for the correct operation and dimensioning of the network cells' apparatuses: a mobile communications terminal operating in macro-diversity uses resources of all the BRSs with which it is simultaneously connected, thus the terminal in macro-diversity uses more resources than those actually necessary for allowing the communications.
A further peculiarity of UMTS networks is that such networks are adapted to provide a plurality of different network services, such as, for example, telephony, fax, video-telephony, Internet access and Web browsing, streaming and so on. Each one of such services generally has characteristics in terms of speed (number of bits per second) and traffic (amount, symmetrical or asymmetrical) that are specific for the service under examination.
The dimensioning of the cells should therefore take into account both the characteristics of each service, and the possible associations of services over a single radio carrier, as provided for by the CDMA/WCDMA access technique.
Moreover, like every cellular radio-mobile system, also a UMTS network has common broadcast control channels in the whole cell area. Such channels contain system information, that are necessary for radio apparatuses (receivers) of the mobile communications terminals.
Due to the networks' peculiarities, the planning of UMTS networks is a complex task, requiring approaches that are substantially different from those used for previous cellular mobile telecommunications networks, particularly second-generation cellular networks like those complying with the Global System for Mobile Communication (GSM) standard, or with the Interim Standard (IS95).
In general, in view of a current network deployment, the planning aims to produce, as results or outputs, the proper positioning of the BRSs in the geographic area under examination, and also allows determining the set of radio-electric cell parameters (e.g., antenna tilt, azimuth of the direction of maximum gain, radio power, etc.) and the allocation of the radio resources assigned to the network operator (for example, radio carriers). Such outputs are determined by the planning process in compliance with planning objectives, such as, for example:                minimum value of territory covered by the network service, within an area under planning;        maximization of the traffic to be managed among those provided within the area under planning.        
Various planning techniques for UMTS networks are known; according to the followed approach, these techniques can be grouped into two different classes: statistical planning techniques and deterministic planning techniques.
Statistical planning techniques are mainly based on an approach of the Montecarlo type (refer for example to the document 3GPP TR 25.942 v3.0.0 2001-06—“RF System Scenarios—Release 1999” specification). The term “Montecarlo simulation” usually denotes a static simulation composed of a set of statistically independent snapshots. After having fixed the scenario being studied, each snapshot consists in realizing a stochastic process generated starting from different distributions of users in the area being examined. At the end of every snapshot, network performance indicators are provided as results, and the procedure ends with the statistical analysis of various performance indicators provided by every snapshot. The number of snapshots shall be enough to guarantee statistical stability for the planning results. This methodology is rather specific, and it is particularly adapted for examining performances of a UMTS network of relatively limited geographic width; owing to its intrinsic slowness, due to the statistical convergence of results, this technique is not suitable for the analysis of UMTS networks intended to cover geographical areas comparable with those of an entire nation, such as, for example, Italy.
Though keeping the characteristic of a static analysis, the deterministic planning techniques systematically take into account all pixels of the territory on which the network will be planned. Differently from statistical methods, the deterministic methods exploit, as input data, a single users distribution, and a single simulation is carried out, without the need of a statistical aggregations of the results. Deterministic planning techniques are more suitable for planning UMTS networks intended to cover relatively large geographical areas, even if the planning result is generally less adherent to the evolving reality.
Irrespective of the approach followed, one of the phases of the methods for planning a cellular mobile telecommunications network of the type herein considered, is the downlink coverage planning/evaluation, also referred to as “power control on the downlink”, i.e. the planning/evaluation of the coverage in the link from the BRSs to the pixels of the area under planning. In this phase, for each cell of the area under planning, the transmission power per traffic channel that the generic cell should deliver is calculated, for each pixel belonging to the service area of that cell and for each network service (i.e., for example, for the telephony, facsimile, video-telephony, Internet access, e.g., Web browsing, services). The service area of a generic cell in respect of a generic network service is meant to include all those pixels for which that cell is the “serving cell”, i.e. the cell that, among all the other possible cells of the area under planning, requires the lowest power in the uplink, i.e. in the link from hypothetical UEs located in those pixels and the BRS of that cell.
If the calculated power, for the generic pixel, exceeds the maximum power that the serving cell can deliver for a traffic channel in respect of the considered network service, that pixel is put “out-of-service” (“outage”) for insufficient power in the downlink.
The set of pixels, belonging to the service area of the generic cell in respect of the generic network service, not being in outage, forms the overall service area of the cell in respect of that network service.
The union of all the overall service areas for all the network services and for all the cells of the area under planning is referred to as the global service area of the network (in the area under planning).
The downlink power control phase also encompass a cell “capacity check” on the downlink: the overall power that, according to the above-mentioned calculations, is estimated to be required to the generic cell is compared to the maximum power that the (power amplifiers of the BRS of the) cell can deliver: if the calculated overall required power exceeds the maximum power that the cell can deliver, the cell does not pass the capacity check, and it might be necessary to modify the traffic distribution and/or the locations of the cells in the area under planning.
In EP 1335616, a method for planning and/or evaluating a downlink coverage in CDMA radio networks is disclosed; the method comprises the steps of: defining a grid on one or more service areas (possibly using a grid definition derived from a planning and/or evaluation of an uplink coverage performed in advance); assigning the cells of the network to pixels defined by the grid (possibly using a cell-to-pixel assignment derived from a planning and/or evaluation of the previously performed uplink coverage); assigning a pilot power to the cells (the pilot power being a fixed proportion of the total transmission power needed for signaling purposes); estimating a desired downlink transmission power for the cells, the downlink transmission power being the sum of the pilot power and of the power for one or more downlink traffic channels; comparing the desired downlink transmission power to a maximum transmission power of the base stations. If it is found that the desired downlink transmission power is larger than the maximum transmission power, one or more changes in the radio network can be made and the planning and/or evaluation of the downlink coverage be restarted.